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METEOR & IMPACT NEWS
By Alastair McBeath, SPA Meteor Section Director

Firstly, a non-meteoric 'impact', that of the publication of ENB Moderator
Professor Roger Griffin's 200th paper on Spectroscopic Binary Orbits
from Photoelectric Radial Velocities, which has just appeared in the
June issue of The Observatory journal (vol. 124, No.1204, pp.176-231;
it also includes 200 references!). ENB Editor Clive Down described the
magnitude of the achievement, and Professor Griffin's long-standing
input to ensure the quality of the ENBs, in ENB 241
http://tinyurl.com/5nchfx . While the papers have no direct bearing on
meteor astronomy, I am delighted to send heartiest congratulations to
Professor Griffin for his accomplishment on behalf of the Section,
because it reinforces that great strides in science come not from
isolated moments of inspiration (important though they may be
sometimes), but from patient, thorough, methodical hard work over
often long periods. As Professor Griffin put it, "Celestial time-scales
are not tailored to human convenience" (p.177), and what we do now
may be of greatest significance only generations hence. Happily, these
papers are already of significance, and look set to continue to be so
as their publication proceeds past this most notable milestone.

Late May saw the "Meteoroid and Meteor Observations as a Basis for
Models" meeting in Huntsville, Alabama, USA, with participation from
several leading amateur meteoricists as well as many professionals in
the field. One main aspect discussed concerned attempts to accurately
determine the near-Earth meteoroid flux, made more difficult because
from the surface, we can only observe those objects large and fast
enough to ablate as meteors, and these need not cover all those
objects potentially dangerous to manned space missions, for instance.
Video and radar work look set to be important in this, the former at
least a field where amateurs can produce significant results. More
amateurs are also urgently required to take part in observing lunar
impact flashes on the Moon from multiple stations, another way of
estimating the numbers of larger meteoroids in the Earth's vicinity.
NASA recently announced they had recorded their 100th such flash
(see:http://tinyurl.com/63khh5 on the SPA's General Chat Forum), and
others are working in this field too (see ENB 239, http://tinyurl.com/6p9d2d).

Another notable topic at the Huntsville meeting concerned the
background sporadic flux of meteors, present throughout the year.
Investigations were presented from International Meteor Organization
amateur video data that showed around 25% of all meteors recorded
were from showers, most of those from the major sources of the
Perseids, Orionids and Geminids, and 75% were sporadics. Of the
sporadics, 15% came from the six sporadic 'sources', long-known from
radar meteor studies, which occupy most of the celestial hemisphere
roughly centred on the direction of the Earth's orbital motion through
space, the "Apex of the Earth's Way", a point on the ecliptic 90
degrees west of the Sun (more details should be available now via
http://www.imonet.org/reports/ ). These sources are the Northern and
Southern Apex, centred about 25 degrees north and south of the actual
Apex point, Helion (on the ecliptic, centred about 15 degrees west of
the Sun), Antihelion (centred about 15 degrees east of the point
opposite the Sun on the ecliptic), and the Northern and Southern
Toroidal sources, centred about 55 degrees above and below the Apex
respectively. Most of these cannot be usefully observed visually, as they
are very diffuse, and even by video, their combined numbers are
clearly small. However, the Antihelion sporadics combine with the
cluster of weak and ill-defined minor shower radiants in this part of the
sky to generate what we now call the Antihelion Source, and this is
visually-detectable. Model simulations presented at the meeting
suggested that about three or four comets have likely contributed most
of the near-ecliptic dust that produces these Antihelion meteors, of
which Comet 2P/Encke was probably the most dominant in past ages,
something that has been long thought. The autumnal Taurid showers
result from relatively much more recent material shed by Comet Encke,
and thus do form a distinct, if broad, meteoroid stream in space.

Speaking of the Taurids, as the centenary of the Tunguska event over
Siberia is nearing on June 30, which has been sometimes linked to
the Taurid Complex of meteoroid streams, comets and asteroids, a
new paper regarding Tunguska was published in April's Terra Nova
journal (Vol. 20, Issue 2, pp.165-168; see Assistant Meteor Director
David Entwistle's General Chat Forum postings recently at:
http://tinyurl.com/2q34qd ). This questioned the claim made last year
that Lake Cheko, about 8 km NNW of the Tunguska airburst's epicentre,
may have been produced by part of the Tunguska object impacting the
surface (featured in ENB 224). News of fresh investigations of the Lake
by the original Italian team are expected later this year.

David Entwistle also spotted another item, concerning the minor August
shower of the Kappa Cygnids, due to reach a peak almost coincident
with full Moon on August 17 this summer. Professional meteoricists
Peter Jenniskens and Jeremie Vaubaillon have suggested the recently-
discovered minor planet 2008 ED9 may be the parent for this shower,
and that it was originally a much larger cometary body that fragmented
sometime between circa 4000 to 1600 BC. They also found that the
stream so-created should produce a far stronger shower for observers
on Venus, were that planet's atmosphere not so opaque and hostile for
surface viewers. It is possible that suitable imaging systems in orbit
about Venus might be able to detect some of the meteors "from above",
however. See David's General Chat Forum posting at:
http://tinyurl.com/6x3o3x for more details.

AMATEUR FINDS FASTEST-SPINNING ASTEROID
New Scientist

An amateur astronomer has discovered the fastest-rotating asteroid
known. The finding came from an educational observatory project and
illustrates how providing the public and schools with professional-
grade telescopes can lead to astronomical discoveries. The asteroid
concerned, known as 2008 HJ, was discovered on April 24 by a robotic
telescope in Socorro, New Mexico. It was then flagged up as an
object for possible observation on the web site of the remotely
controlled 2-m Faulkes telescope at Siding Spring in Australia. The
asteroid was visible only for a few days as it came within 2.8 lunar
distances of the Earth, travelling at a relative speed of about
45 km/s.

Richard Miles, a Dorset-based retired petrochemical researcher and a
Vice-President (and recent President) of the British Astronomical
Association, measured the spin rate of 2008 HJ on April 29. Exposures
of a few seconds showed telltale changes in brightness as the oblong
asteroid turned, each face reflecting sunlight differently. The
pattern revealed that the asteroid revolves once every 42.7 seconds;
the International Astronomical Union has since confirmed the
discovery. The previously-known fastest was 2000 DO8, which rotates
once every 78 seconds. Miles's observations suggest that 2008 HJ is a
compact stony object some 12 metres by 24 metres, with a probable
mass of more than 5000 tons.

SUPERGIANT STAR HAS THICK BELT
ESO

Astronomers in Chile have used the VLT interferometer, which combines
the signals from the 8.2-m 'unit telescopes' in pairs. to observe a
red supergiant star known as WOH G64 which lies 170,000 light years
away in the Large Magellanic Cloud. The star is nearly 2000 times the
radius of the Sun. Its evolutionary status has been in doubt; it was
formerly thought to have started with a mass of 40 solar masses but
the new observations suggest 25, and are more easily explained. The
main difference is that it was assumed that the gas and dust that
surround the star were more or less spherically distributed, whereas
now their structure has actually been resolved and shown to consist of
a ring rather than a shell. The ring has a radial extent from 15 to
250 stellar radii around the star. The object appears to be in an
unstable phase involving heavy mass loss, and astronomers estimate
that the belt of gas and dust that surrounds it contains between 3 and
9 solar masses, which means that the star has already lost a
significant proportion of its initial mass.

MEASUREMENTS SUGGEST A LESS MASSIVE MILKY WAY
SDSS-II

It has been proposed that the Milky Way galaxy is not as massive as
has been thought -- that it has less dark matter than previously
believed, but also that it was more efficient in converting its
original supply of hydrogen and helium into stars. The discovery is
based on data from SEGUE, a large survey of stars in the Milky Way --
one of three programmes that comprise the second Sloan digital sky
survey (SDSS-II). Using SEGUE measurements of stellar velocities in
the outer halo of the Milky Way, the researchers inferred the mass of
the Galaxy from the gravitational field required to keep the stars in
orbit. Some of that field comes from the Milky Way stars themselves,
but much of it comes from an extended distribution of invisible
matter, whose nature has not been satisfactorily identified. To trace
the mass distribution of the Galaxy, the SEGUE team used a sample of
2,400 stars of a type whose distances can be determined from their
measured brightnesses. The stars concerned are luminous enough to be
seen to large distances, enabling the team to measure velocities of
stars out to distances of 180,000 light-years from the Sun.

The most recent previous studies of the mass of the Milky Way used
mixed samples of 50 to 500 objects. They implied masses up to
2 x 10*12 (two million million) times the mass of the Sun, but when
the SDSS-II measurement within 180,000 light-years is corrected to a
total-mass measurement, it yields a value slightly under 1 x 10*12.

The SPA Electronic News Bulletins are sponsored by the Open University.

Bulletin compiled by Clive Down

(c) 2008 the Society for Popular Astronomy

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